1. Field of the Invention
The present invention is related to non-destructive inspection equipment, and more particularly, to a loading device that applies a normal load to a composite structure being non-destructively inspected.
2. Description of Related Art
Non-destructive inspection of structures involves examining a structure without harming the structure or requiring significant disassembly of the structure. Non-destructive inspection is advantageous for many applications in which a thorough inspection of the exterior and/or interior of a structure is required. For example, non-destructive inspection is commonly utilized in the aircraft industry to inspect aircraft structures for any type of internal or external damage to the structure.
Among the structures that are routinely non-destructively tested are composite structures. In this regard, composite structures are commonly used throughout industry because of their engineering qualities, design flexibility, and low weight. As such, it is frequently desirable to inspect composite structures to identify any flaws, such as cracks, voids, or porosity that could adversely affect the performance of the composite structure.
Various types of sensors may be utilized to perform non-destructive inspections. One or more sensors may move over the area of the structure to be examined, and receive data regarding the structure. For example, a pulse-echo, thru-transmission, or shear wave sensor may be utilized to obtain ultrasonic data, such as thickness gauging, detection of laminar defects and porosity, and/or detection of cracks in the structure. Resonance, pulse echo, or mechanical impedance sensors may be utilized to provide indications of voids or porosity, such as in adhesive bondlines of the structure. The data acquired by the sensors is typically processed by a processing element, and the processed data may be presented to a user via a display or stored for subsequent analysis.
Certain internal flaws are more readily detectable when the structure being inspected is loaded so that the internal flaws become more apparent to the non-destructive inspection instruments. These internal flaws may include weak bonds that will separate when loaded or may include incomplete bonds between layers that contact one another when experiencing no load but that also readily separate once loaded. An applied load can also be used to counteract a preload on the structure to improve the inspection of the structure.
Existing loading devices use various techniques to apply a load to a structure being inspected. One destructive method of applying a load is to adhesively bond a button or other feature to a surface of the structure and cutting a portion of the structure around the adhered button. An instrument pulls the button until the portion of the structure adhered to the button breaks away from the structure, such that the maximum load indicates the structural strength of the structure but leaves a hole in the structure that must be repaired.
One non-destructive method of applying a load uses electromechanical means to magnetically apply a load to a ferromagnetic layer or portion of a structure being inspected. Such methods are limited to structures that include ferromagnetic materials since a magnet is needed to engage the structure. Unfortunately, this method is generally unsuitable for composite structures since many composites do not comprise ferromagnetic materials. A further non-destructive method consists of applying a vacuum to a surface of the structure to measure surface deformation that indicates internal or external flaws. Such vacuum stress systems require a relatively large suction area, which may limit access to the surface of the structure requiring inspection. In addition, such vacuum stress systems are not able to create a suction on a surface that defines protrusions because such protrusions would compromise the seal of the suction.
Accordingly, a need exists for a loading device for conveniently applying a load to a surface of a composite structure for non-destructive inspection. A need also exists for a loading device that can apply a load to a surface of a structure that defines protrusions.